1. Field of the Invention
The present invention relates to a wet process for removing a specific component from a gas containing the same. More specifically, it relates to a wet process for removing a specific component such as a specific gas component or a specific solid particle from a gas containing the same by using a scrubbing column provided with at least one Moredana plate.
The term "Moredana plate" as used in this specification means a perforated plate or grid plate without weir and downcomer.
2. Description of the Prior Art
Typical wet processes for the removal of a specific component from a gas containing the same include, for example, those of the type wherein the gas to be treated is brought into countercurrent contact with a scrubbing liquid by means of a conventional perforated plate column provided with perforated plates having a free-space ratio of less than 0.30, a packed column, a spray scrubber, a bubble-cap tray column or the like.
However, the process employing a packed column has the following disadvantages: occurrences of channeling of liquid and gas streams in the packed column and occurrences of plugging or blocking in the packed column during operation when the gas or liquid contains solid materials, dust particles or the like. The process employing a spray scrubber has the following disadvantages: requirement of a large amount of power to spray the liquid, likely occurrence of liquid entrainment and an unsatisfactory absorption capacity.
The processes employing a plate column such as, for example, a bubble-cap tray column, a conventional perforated plate column and the like also have some disadvantages in that the pressure drop of the column is relatively high and the plate efficiency of the plate column is usually low. In addition, the superficial gas velocity in such plate column is generally limited to the range of from approximately 0.3 m/sec to approximately 2 m/sec in conventional scrubbing columns. Accordingly, in order to treat a large flow rate of gases, a large column is required. Therefore, the development of gas scrubbing processes having a high gas capacity has been eagerly desired in the industry.
In order to obviate the above-mentioned problems in the conventional gas scrubbing processes, two of the three inventors of the present invention have developed and proposed a process for removing a specific gas component and/or fine dust from gas comprising passing the gas containing the specific gas component and/or fine dust upwardly through a plate column comprising at least one perforated or grid plate without weir and downcomer and having a free-space ratio (Fc) of 0.25 to 0.60 at a superficial gas velocity falling within an undulation region, while passing a liquid absorbent downwardly through the plate column in a countercurrent flow relationship to the upflowing gas under a liquid-gas ratio (L/G) of 0.5 or more. This process is disclosed in Japanese Patent Publication No. 51-31036(1976) (published on Sept. 4, 1976) and U.S. Pat. No. 3,941,572 (issued on Mar. 2, 1976). The term undulation region mentioned above is also defined in the above publications. Stated in these publications are the following six equations for calculating Ugm (i.e., the minimum superficial gas velocity of the undulation region) and Ugc (i.e., the maximum superficial gas velocity of the undulation region) under a liquid flow rate of from 9,000 to 110,000 kg/m.sup.2 .multidot.hr. Four of the six equations are as follows: ##EQU1## wherein g=gravitational acceleration (m/sec.sup.2)
Fc=free-space ratio of perforated plate and grid plate (-) PA1 L=liquid flow rate (kg/m.sup.2 sec) PA1 G=gas flow rate (kg/m.sup.2 sec) PA1 .rho.l=liquid density (kg/m.sup.3) PA1 .rho.g=gas density (kg/m.sup.3) PA1 l=.sqroot.2.sigma./g.rho.l=capillary constant (m) PA1 .sigma.=surface tension (kg/sec.sup.2)
The above equation (1) is applicable to the perforated plate in the case of EQU Fc.gtoreq.0.16 and .rho.g/.rho.l .times.10.sup.3 .gtoreq.0.838,
and the equation (2) is applicable to the perforated plate in the case of EQU Fc.gtoreq.0.16 and .rho.g/.rho.l.times.10.sup.3 .ltoreq.0.838,
the equations (3) and (4) are applicable to perforated plate (Fc.ltoreq.0.16) and grid plate, when EQU .rho.g/.rho.l.times.10.sup.3 .gtoreq.1.20 and .rho.g/.rho.l.times.10.sup.3 .ltoreq.1.20,
respectively.
The remaining two equations are as follows: EQU Ugc/Ugm=7.509.times.10.sup.2 .times.L.sup.-0.5704 ( 5) EQU Ugc/Ugm=3.434.times.L.sup.-0.0807 ( 6)
wherein L is the same in equations (1) through (4).
The above equations (5) and (6) are applicable to the perforated or grid plate, when L=6.times.10.sup.4 .about.11.times.10.sup.4 kg/m.sup.2 .multidot.hr and L=10.sup.4 .about.6.times.10.sup.4 kg/m.sup.2 .multidot.hr, respectively.
The above-mentioned problems of the conventional gas scrubbing processes can be obviated to some extent by contacting a gas with a scrubbing liquid under the conditions of a superficial gas velocity being within the range of from Ugm to Ugc and a liquid flow rate being within the range of from 9,000 to 110,000 kg/m.sup.2 .multidot.hr according to the process proposed above. However, this process is still insufficient in terms of being used as practical industrial processes, especially in the case where a large amount of a scrubbing liquid, for example, 110,000 kg/m.sup.2 .multidot.hr or more is used. For instance, 110,000 kg/m.sup.2 .multidot.hr or more of a scrubbing liquid are required for industrial processes in the case where a high content (e.g. 1000 ppm or more) of sulfur oxides present in a waste gas is treated with a scrubbing liquid containing calcium carbonate.